1. Field of the Invention
The present invention relates to a camera shake correction technique.
2. Description of the Related Art
A recent increase in the quality and zooming ratio of an image sensing device has posed a problem of blur of a sensed image caused by camera shake upon image sensing, and conventionally led to wide use of image sensing devices with a camera shake correction function. Such an image sensing device with a camera shake correction function generally adopts an optical camera shake correction method of optically correcting a camera shake using a gyro sensor configured to detect an angular velocity dependent on a camera shake and a driving device configured to control the relative positions of the lens and image sensor so as to cancel the camera shake.
A method of correcting a camera shake by image processing is also under study. As a method of correcting a camera shake for one blurred image, it is known to interpret the process of image degradation caused by a camera shake as convolution using a filter, calculate a filter based on the camera shake speed, and remove the influence of camera shake by deconvolution (patent literature 1 (US-2007-0258706)).
In general, the frequency characteristic of the blur filter has a property of becoming 0 at a given frequency. This results in a problem of losing information about the frequency at which the frequency characteristic becomes 0. To solve this, there is proposed a technique of opening/closing a shutter at random at the time of exposure when one image is acquired, and correcting a camera shake or object blur by arithmetic processing using the shutter opening/closing information (patent literature 2 (Japanese Patent Laid-Open No. 2008-310797)). This technique is called coded exposure. A pattern used to open/close the shutter at random in exposure is called a coded exposure pattern. In patent literature 2, blur correction is implemented using a satisfactory coded exposure pattern to prevent the frequency characteristic of the blur filter from becoming 0.
The techniques disclosed in the patent literatures cited as examples use a rectangular wave for the coded exposure pattern when executing coded exposure. However, an image sensor mounted in a general digital camera adopts photoelectric conversion, and generates an electrical signal from light entering the image sensor. Hence, a signal is not output in the form of a rectangular wave from an actual image sensor and has a time lag. If this signal is regarded as a rectangular wave output and blur correction calculation is done, a blur-corrected image degrades.